By Sam Kim SEOUL, Nov. 10 (Yonhap) -- A North Korea naval boat returned home "wrapped in flames" after a brief but fierce skirmish in the South Korean waters off the west coast on Tuesday, Seoul officials said.

North Korea disputed the account, saying in a statement that the South must apologize for shooting at its boat as it returned to port after conducting a routine mission in its waters.

No South Korean sailors were killed in the clash that erupted shortly after the North Korean patrol boat crossed the Northern Limit Line (NLL) at 11:27 a.m. in the Yellow Sea, the officials here said.

The shooting lasted about two minutes, Lee Ki-shik, a South Korean military officer told reporters, with the South Korean boat taking about 15 shots from the North Koreans that apparently fired about 50 rounds.

South Korea retaliated by firing back with its onboard guns, Lee said, adding his government expresses regret over the incident -- the third such clash in the area after 1999 and 2002.

South Korean Prime Minister Chung Un-chan told lawmakers in a televised parliamentary meeting that a single North Korean boat returned across the border while "enveloped in flames."

He also said the incident was "accidental." President Lee Myung-bak convened an emergency national security meeting, calling for "composure" in dealing with the situation.

The South Korean Navy sounded a warning twice before the North Korean boat crossed the NLL -- a de facto border drawn at the end of the Korean War -- and three times afterward, according to Lee Ki-shik.

The naval boats were a little over 3km away from each other, Lee said, stressing the South Korean Navy followed standard operating procedure before the shooting erupted.

South Korean analysts gave mixed views about North Korea's possible motive behind the incident, which took place only a week ahead of an Asian trip by U.S. President Barack Obama.

"It appears to be a move to raise tension ahead of Obama's visit to South Korea," Yoo Ho-yeol a North Korea professor at Korea University in Seoul. "North Koreans believe tension helps them strengthen their bargaining power."

Ryu Gil-jae, professor at the University of North Korean Studies in Seoul, disagreed, saying the incident appeared aimed at testing the South Korean government.

"North Korea would have test-fired missiles if it had wanted to vex the U.S.," he said. "The Yellow Sea clash is more of a message to the South that it should be taken more seriously."

The clash came amid an accelerating thaw between the Koreas, whose relations turned frosty following the inauguration of South Korean President Lee Myung-bak early last year.

Kang Sung-yoon, a North Korea specialist at Seoul's Dongguk University, said the North Korean attack on the South appears to serve more than one purpose.

But Kang warned against reaching a quick conclusion on the issue, saying the battle should be more closely examined in the first place.

"Details regarding the incident should be looked at to understand what the North Korean intent really was," he said.

South Korea recently deployed its latest high-speed guided-missile boat along the NLL, which was drawn by a U.S. general at the end of the 1950-53 Korean War that ended in a truce.

"We are analyzing the motive for the North Korean boat's crossing. We do not rule out the possibility that the clash may have been an accidental skirmish," a defense official here said, asking for anonymity.